That feeling: When you see a piece of code and you're like "I can do that in half the number of lines..."
And so you spend the next 45 minutes redoing something that was working perfectly.
Except now it's a convoluted and unreadable demon child that appears to writhe on the screen before your very eyes and cause madness and hatred in all who view it. But.. it works in 3 lines now instead of 7... and you don't need 4 of those local variables that you did before... and even though it's completely impractical because no sane mortal (including yourself - barely) can actually read it, it's still yours and you're proud of it.